with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve shows multiple peaks
with a duration of about 30 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~4 sec after the trigger.
Due to an observing constraint, Swift will not slew until T0+43.3
minutes. There will be no XRT or UVOT data until this time.
Burst Advocate for this burst is D. Malesani (malesani AT dark-cosmology.dk).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)

with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 19 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper.
A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.70 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 7.6
(+2.39/-2.15) x 10^21 cm^-2 (90% confidence).

with an uncertainty of 1.5 arcsec (radius, 90% confidence).
This position may be improved as more data are received. The latest
position can be viewed at http://www.swift.ac.uk/xrt_positions. Position
enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans
et al. (2009, MNRAS, 397, 1177).
This circular was automatically generated, and is an official product of the
Swift-XRT team.

If the light curve continues to decay with a power-law decay index of
1.28, the count rate at T+24 hours will be 0.021 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x
10^-13 (1.4 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00690598.
This circular is an official product of the Swift-XRT team.

with an uncertainty of 1.2 arcmin, (radius, sys+stat, 90% containment).
The partial coding was 45%.
The mask-weighted light curve shows a single episode with several overlapping
pulses. The emission starts at T-15 sec, peaks at T+3 sec and ends at T+20 sec.
T90 (15-350 keV) is 34.1 +- 5.6 sec (estimated error including systematics).
A pre-planned spacecraft slew moved the source out of the field of view at
about T+165 sec.
The time-averaged spectrum from T-31.38 to T+10.37 sec is best fit by a simple
power-law model. The power law index of the time-averaged spectrum is
1.67 +- 0.12. The fluence in the 15-150 keV band is 1.7 +- 0.1 x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+2.84 sec in the 15-150 keV band
is 2.0 +- 0.3 ph/cm2/sec. All the quoted errors are at the 90% confidence
level.
The results of the batgrbproduct analysis are available at
http://gcn.gsfc.nasa.gov/notices_s/690598/BA/

GCN Circular #19530
M. De Pasquale (UCL-MSSL) and D. Malesani (DARK/NBI)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 160611A
2687 s after the BAT trigger (Malesani et al., GCN Circ. 19522).
Very close to the XRT error circle (Osborne et al. GCN Circ. 19523), two
sources are detected in the UVOT images. These sources are also detected
in the Digitized Sky Survey (DSS) and are listed in the USNO catalog.
Their light would blend with any new source at the XRT position, making
the analysis more delicate.
None of the two sources shows any significant flux decrease in the white
filter between the first two white exposures (mid-time: 3071 s after
the trigger) and the last three white exposures (mid-time: 10030 s after
the trigger). Similarly, we find no significant decrease of the flux
of the two sources in the u filter between the first u filter exposure
(mid-time: 2946 s) and the last one (mid-time: 8560 s).
We conclude that no optical afterglow consistent with the XRT position
is detected in the UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) are: